<!DOCTYPE html>
<html>
<head>
<script>
addEventListener("load", () => {
  const object = document.querySelector("object[contenteditable]");
  const mo = object.querySelector("mo");
  const range = new Range();
  document.replaceChildren();
  range.insertNode(object);
  object.replaceChild(mo, object.firstChild);
});
</script>
</head>
<object contenteditable>
  <mo>
  </mo>
</object>
</html>
